Balloon Kebab

From the kitchen of Jamie Oliver they are not. However, these balloon kebabs are guaranteed to go down a treat at your next BBQ - we’re told they taste a lot like rubber chicken.

Australian Curriculum links

  • Science > Science Inquiry Skills > Year 1 > ACSIS024
  • Science > Chemical Sciences > Year 4 > ACSSU074
  • Science > Physical Sciences > Year 5 > ACSSU077

You'll need

  • two half-inflated balloons
  • bamboo skewer

Try this

  1. Hold a balloon in one hand and the skewer in the other.
  2. Try and push the skewer through the side of the balloon. (It will pop.)
  3. Get another balloon and try again, but this time carefully push the skewer through the balloon at the neck of the balloon, next to the knot.
  4. If the balloon doesn’t pop, line the point of the skewer up with circle of darker rubber at the top of the balloon and very carefully push the skewer through.

What's happening?

Balloons are made of rubber and rubber is elastic. When you stretch something that’s elastic it will spring back to the same shape it was before you stretched it. When you blow up a balloon you’re causing most of the rubber of the balloon to become very tightly stretched. Poking a skewer into the side of the balloon tears the rubber; it quickly springs apart and the balloon pops. However, at the neck and top of the balloon the rubber isn’t as tightly stretched. When you push the skewer through the balloon at those points the rubber simply folds around the skewer and the balloon doesn’t pop.

Rubber is an example of a polymer - a type of material made up of lots and lots and lots (sometimes millions) of repeating units. It’s similar to a really long chain except that it’s all tangled up. Smaller sections of the ‘chain’ called cross-links stretch between the longer pieces of ‘chain’ holding everything together. When you blow up a balloon the force of the air inside the balloon causes the rubber to stretch and all of the pieces of the ‘chain’ to move apart from each other. Because all the pieces of rubber in our balloon are pulling in different directions when you pushed the skewer through the side of the balloon it only needed to take out a few links in the polymer chain for the balloon to rip apart and pop.

You can imagine that the stretched rubber in the balloon is actually a whole bunch of people holding hands that are pulling in different directions at the same time. Everyone is pulling so strongly that if a few people let go, the small holes that would form in our tangled and stretched ‘chain’ would quickly become large holes. Once there is one hole, more and more people would let go of each other because of the force pulling them in opposite directions. Eventually, everyone flies off in the direction they were pulling, probably falling over and scraping their knees.

Real world links

The loud BANG an over-inflated balloon makes when it pops is actually a series of sonic booms! A sonic boom is the loud booming sound that accompanies something – such as an aeroplane – travelling faster than the speed of sound (340 m/s in air at sea level). When you blow up a balloon until it can’t be blown up any more the rubber becomes extremely tightly stretched. When a little bit more air is added and the balloon finally pops, the tears that travel through the rubber can actually move faster than the speed of sound!